There will be two phases of gold-making in Wrath of the Lich King.
In the beginning, as soon as the patch is out, many folks will be power-leveling their professions to the new max. Some are already trying to acquire recipes and mats that will take their profession to the cap.
GATHER, GATHER, GATHER!! In particular, mining and herbalism will be huge in the beginning. Demand for ore and herbs will skyrocket and you’ll be able to set and command a high price. If you are strictly interested in making gold, I recommend those two gathering professions…at least until the economy stabilizes.
After things settle, and your server gets a healthy population of level 80s, the end-game view of professions will be to have the more rare recipes on your servers. These will be obtained by doing the daily quests for those professions, collecting the tokens and using them to get the unique recipes.
Having said that, there is still a risk with that. Unless you can start collecting tokens from Day One, other crafters will be ahead of you in what recipes they can obtain. So if you only have one level 80 toon, and you aren’t doing a crafting profession’s daily quests from the very beginning, other crafters will snag the good recipes. In addition, even if you are the first to get the rare recipes, there will always be others who catch up to you (or have more time to grind than you do), who will eventually undercut you. So, if you’re banking on being the only one on a server with a recipe, you’re rolling the dice.
There will always, ALWAYS be a need for gathered items. Gold-makers know this, and collect like crazy, and other than manipulating the Auction House, it’s the most secure way of making gold repeatedly.
If you have read through this entire site, you know this advice already, but: get on thottbot.com (the beta side), and find out what mats will be used, and in what quantities, to level up the crafting professions. Stock up on those mats, because in the first few days, you won’t be able to keep them on the AH, regardless of how much you price gouge!